title: The combined organ effect: protection against rejection?
abstract: OBJECTIVE
  To further our understanding of the potential protective effects of one organ allograft for another in combined organ transplants by comparing rejection-free survival and the 1-year rejection rate of each type of combined organ transplant.
  
  
  BACKGROUND
  Liver allografts have been thought to be immunoprotective of other donor-specific allografts. Recent observations have extended this property to other organs.
  
  
  METHODS
  Analysis of data from the United Network of Organ Sharing included recipients 18 years or older (except those receiving intestinal transplants) transplanted between January 1, 1994, and October 6, 2005, and excluded those with a previous transplant (n = 45,306), live-donor transplant (n = 80,850), or insufficient follow-up (n = 4304). Patients were followed from transplant until death (n = 41,524), retransplantation (n = 4649), or last follow-up (n = 87,243).
  
  
  RESULTS
  A total of 133,416 patients were analyzed. Rejection rates for allografts co-transplanted with donor-specific primary liver, kidney, and heart allografts are significantly lower than rejection rates for allografts transplanted alone. Allografts accompanying primary intestinal or pancreatic allografts did not have reduced rejection rates. A decreased rate of rejection was seen in interval kidney-heart transplants when allografts shared partial antigenic identity. Decreased rates of rejection were also seen in transplants of 2 donor-specific organs of the same type.
  
  
  CONCLUSIONS
  In combined simultaneous transplants, heart, liver, and kidney allografts are themselves protected and protect the other organ from rejection. Analysis of interval heart-kidney allografts suggests the need for partial antigenic identity between organs for the immunoprotection to take effect. This was not demonstrated in interval liver-kidney transplants. Increased antigen load of identical antigens, as seen in double-lung and double-kidney transplants, also offers immunologic protection against rejection.
authors.affiliation: Division of Transplant Surgery, Department of Surgery, Columbia University College of Physicians and Surgeons, New York, New York 10032, USA. aar2107@columbia.edu
authors.forename: Abbas
authors.initials: A
authors.lastname: Rana
authors.forename: Susanne
authors.initials: S
authors.lastname: Robles
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Russo
authors.forename: Karim J
authors.initials: KJ
authors.lastname: Halazun
authors.forename: David C
authors.initials: DC
authors.lastname: Woodland
authors.forename: Piotr
authors.initials: P
authors.lastname: Witkowski
authors.forename: Lloyd E
authors.initials: LE
authors.lastname: Ratner
authors.forename: Mark A
authors.initials: MA
authors.lastname: Hardy
mesh_terms: D000328:Adult; D005260:Female; D006084:Graft Rejection / Q000453:epidemiology / Q000276:immunology* / Q000517:prevention & control; D016027:Heart Transplantation / Q000276:immunology*; D006801:Humans; D053208:Kaplan-Meier Estimate; D016030:Kidney Transplantation / Q000276:immunology*; D016031:Liver Transplantation / Q000276:immunology*; D008297:Male; D008875:Middle Aged; D012042:Registries / Q000706:statistics & numerical data; D014184:Transplantation, Homologous; D014481:United States / Q000453:epidemiology